Acquisition and processing of data
Three matrix files of CAVD samples, which include GSE12644, GSE51472, and GSE83453, are all from the GEO (https://www.ncbi.nlm.nih.go-v/geo/). GSE12644, based on GPL570, is composed of 10 normal and 10 calcified aortic valves. GSE51472, based on GPL570, contains 5 normal, 5 sclerotic, and 5 calcified aortic valves. GSE83453, based on GPL10558, including 8 normal and 9 calcified aortic valves. To analyze more accurately, five sclerotic valve samples were removed from GSE51472. Currently, the most prevalent m6A methylation regulators consist of WTAP, KIAA1429, ZC3H13, RBM15, RBM15B, BLL1, METTL3, METTL14, METTL16, YTHDC1, YTHDC2, YTHDF1, YTHDF2, YTHDF3, HNRNPC, FMR1, LRPPRC, HNRNPA2B1, IGFBP1, IGFBP2, IGFBP3, ELAVL1, IGF2BP1, FTO, ALKBH5, RBMX are regarded as common m6A regulators. To screen m6A regulators, the “limma” package was utilized to analyze samples from 3 datasets (|LogFC| >2 and P<0.05). Heatmap diagrams were created to show the expression of m6A regulators in calcified and normal aortic valves. Following that, differentially expressed m6a in three datasets was defined as key CAVD-related m6A regulators.
Enrichment analysis of target genes of key CAVD-related m6A regulators
M6A2Target (http:// m6A2target.canceromics.org) was utilized to find the targets of key CAVD-related m6A. Based on GSE12644, Pearson correlation analysis was performed to identify co-expressed genes in CAVD (|R| >0.9 and P<0.01). Target genes regulated by key m6A were selected when predicted targets and co-expressed genes were intersected. Then, Metascape was performed to functionally annotate genes regulated by key m6A. (http://Metascape.org/gp/index.html#/main/step1)
Immune Infiltration Analysis
CIBERSORT was utilized to analyze immune cell infiltration in CAVD, evaluated immune cell infiltration ratios, and constructed a bar graph for visual display. A comparison of infiltration of 22 kinds of immune cells into CAVD patients and healthy people was conducted using “vioplot” package. The correlation heatmap was then constructed using the "corrplot" tool to highlight the correlation of the 22 various types of invading immune cells. Spearman's rank examined the relationship between immune cells and a key m6A regulator. Finally, the "ggplot2" package was used to visualize the plot. P < 0.05 indicated statistically significant.
Competitive endogenous RNA (ceRNA) network
LncRNA modulates mRNA expression of encoded proteins by competing with mRNA for combining with miRNA. Based on this mechanism, we constructed the ceRNA network. The selection of differential Expressed lncRNAs and mRNAs in GSE12644 was performed by the “limma” package(P<0.05 and |log2FC|>1) and the DElncRNA-miRNA interaction was predicted by miRcode (http://www.mircode.org). Furthermore, we projected the potential target gene mRNA of miRNA using two online data bases: Targetscan (http://www.targetscan.org), and miRDB (http://www.mirdb.org). The differentially expressed mRNA was interacted with the target mRNA of the miRNA to obtain the miRNA-mRNA gene pool. Finally, we used Cytoscape software v3.8.1 to establish the corresponding lncRNA-miRNA-mRNA interaction network and visualize it. We did further research by crossing mRNA in ceRNA with target genes regulated by key CAVD-related m6A regulators to find their shared genes. The shared gene-related pathway may be a possible mechanism of m6A in CAVD.
Experimental design and qRT-PCR
Our specimens were from the Affiliated Hospital of Xuzhou Medical University, including 3 calcified aortic valves and 3 normal aortic valves. Three cases of calcified aortic valve were from men who underwent aortic valve replacement. Three normal samples were from aortic valve insufficiency due to mechanical stress in ascending aortic aneurysm. Senior pathologists examined all valve samples. Clinical information of these patients was provided in Supplement2. First, we made the specimens into tissue homogenate and then extracted the total RNA from our specimens by Trizol reagent (Invirogen). Secondly, the iScriptTM cDNA Synthesis Kit (Bio-Rad Laboratories, Hercules, CA, USA) was used for reverse transcription of the extracted total RNA to synthesize complementary DNA. Primers were designed and synthesized by Shanghai Generay Biotech Co, Ltd, and primer sequences could be found in Supplement2. Finally, a PCR reaction system was established. Details on the PCR primer sequences and their results can be obtained from the supplementary documentation.
Statistical analysis
Normal distributions are reported as mean ± standard deviation, non-normal distributions as median, and classification variables as percentages. Comparison of two groups using the t-test, Fisher test. Statistical analysis is conducted by SPSS 24.0 (IBM, Amunk, New York, USA) and Prism 7.0 (GraphPad, San Diego, CA, USA). P < 0.05 was considered statistically significant.